1. Field
One or more embodiments of the present invention relate to a beta alumina solid electrolyte that is used in a thermoelectric converter, a battery, a sensor, and a display; and a method of preparing the beta alumina solid electrolyte.
2. Description of the Related Art
Beta alumina has high sodium ion conductivity, and due to the high sodium ion conductivity, beta alumina is used as a solid electrolyte for use in an alkali metal thermoelectric converter, a sodium-based secondary battery, such as a Na—S secondary battery, and various sensors and displays.
A beta alumina is represented by Na2O.xAl2O3 (where x is from 5 to 11), and is present in two different crystal structures of β-alumina and β″-alumina. In general, a beta alumina includes β-alumina, β″-alumina, or a mixture thereof. Also, since β″-alumina has much higher sodium ion conductivity than β-alumina, β″-alumina or a mixture including β″-alumina and β-alumina is often used as a solid electrolyte.
The beta alumina may be prepared by using a solid state method in which powder of oxides, such as Na2O or Al2O3, are mixed and the mixture is sintered. However, when the solid state method is used to prepare beta-alumina, the beta alumina may have a low sintering density and a high porosity and thus, Na is concentrated near pores, and thus, the beta alumina has low durability and low electrical characteristics. In addition, since the solid state method is used at a high temperature, a great concentration of Na may evaporate during sintering, and thus, it is difficult to embody a desired (target) composition.
Accordingly, there is a need to develop a method of preparing beta alumina that provides a solid electrolyte having high density in which evaporation of Na during sintering is suppressed.